The present invention related to a magnetic tape cassette, and more particularly to a magnetic tape cassette suited for use in a digital audio tape recorder (DAT).
Recently, cassette tape recorders have become very compact in size and lightweight, and magnetic tape cassettes of a compact size for such tape recorders have now been extensively used. In the field of audio equipment, the above-mentioned DAT has been developed (see, for example, ELECTRONICS, June 1987, pages 65-70), and this has enabled long recording and playback times of high quality and high density.
Magnetic tape cassettes, which are capable of recording and playback over a relatively wide frequency band as is the case with conventional video tape cassettes, have been developed for use in DATs. With respect to the appearance and configuration of such magnetic tape cassettes for a DAT, they are more compact in size and handier to carry than conventional audio compact cassettes.
As a result, magnetic tape cassettes for DATs tend to be carried around and used outdoors as frequently as or more frequently than conventional audio compact cassettes.
As is well known, in a DAT analog signals are converted into digital signals to effect recording. Therefore, if the magnetic tape has a minute flaw or dust is lodged thereon, signal dropout can occur. To reduce the chances of this occurring, such magnetic tape cassettes are generally provided with a special dust prevention mechanism.
In one example of such a special dust prevention mechanism, there are provided at the bottom of the cassette a slider and a lock mechanism for the slider. When the magnetic tape cassette is placed in use, the slider is moved in sliding contact with the bottom surface of the cassette half to open the lower side of an opening provided at the front side of the cassette to expose the magnetic tape so that the magnetic tape can be pulled out from the cassette and placed in contact with a magnetic head. When the magnetic tape cassette is not in use, the slider is returned, in sliding contact with the bottom surface of the cassette, to retract the magnetic tape into the cassette, that is, to its sealed condition, thus closing the lower side of the opening.
Generally, the cassette case composed of two cassette halves is made of an ABS resin and a polystyrene (PS) resin, and in most cases the slider is made of a polyoxymethylene (POM) resin. POM resin is harder than acrylonitrile butadiene styrene (ABS) resin and PS resin, and therefore if the slider is reciprocally moved repeatedly as described above over a prolonged period of time, the bottom surface of the cassette half tends to wear due to friction between the two components.
The rubbed-off powder produced as a result of this action adheres to the magnetic tape at the point where it runs on the slider, resulting in signal dropout.
In view of the above, it has conventionally been proposed to provide projections or stepped sections on the contacting surface between the cassette half and the slider to decrease the area of contact between the two in an attempt to reduce the production of such powder. With this arrangement, however, satisfactory results could not be obtained. Thus, it has been desired to provide an arrangement by which high-level recording and playback with high density recording can be maintained over a prolonged period of time.
The invention further relates to a magnetic tape cassette in which a magnetic tape wound around a pair of hubs is supported within a cassette case so that the magnetic tape can be run to effect recording and playback.
In video equipment, such as a video tape recorder or an audio tape recorder, there have been extensively used magnetic tape cassettes in which a magnetic tape wound around a pair of hubs is supported within a cassette case in such a manner that the magnetic tape can be run to effect recording and playback. Such a magnetic tape cassette when in use is loaded into a cassette loading portion of a recording and playback device, that is, a video tape recorder or an audio tape recorder. Since the magnetic tape must be disposed in proper contact with the magnetic head of the recording and playback device, it is necessary to accurately position the cassette case with respect to the cassette loading portion when the former is loaded in position into the latter.
A positioning method used, for example, with an audio magnetic tape cassette 220 will now be described with reference to FIG. 1. A cassette loading portion 205 defined by a recessed portion of a tape recorder body 201 is covered by a bucket 202 pivotally movable to one end thereof. Mounted on a chassis 206 of the cassette loading portion 205 are a pair of reel shafts 209 which are inserted in respective reel shaft insertion holes 223 of the magnetic tape cassette 220 when the cassette is loaded. Capstan 208 is also mounted on the chassis 206 and cooperates with a pinch roller 211 disposed in opposed relation thereto so as to hold the magnetic tape 224 therebetween to run the same at a constant speed. The pinch roller 211, a recording and playback head 212, and an erasing head 213 are linearly arranged on a movable chassis 210, and these components are introduced into openings 225 and 226 formed in the front end of the loaded magnetic tape cassette 220 when the movable chassis 210 is driven in the direction of an arrow A for effecting a recording and playback.
Two metal positioning pins 207a and 207b are fixedly mounted on the chassis 206 near the recording and playback head 212, the pins 207a and 207b extending in the direction of thickness of the loaded cassette.
The magnetic tape cassette 220 has positioning holes 221 and 221b disposed near the opening 225 which open in the direction of thickness of the cassette, the positioning pins 207a and 207b being adapted to be inserted into the positioning holes 221a and 221b, respectively. The magnetic tape cassette also has capstan insertion holes 222 formed near the openings 226 and opening in the direction of thickness of the cassette, the capstan 208 being loosely fitted in the capstan insertion hole 222.
Through a manual or an automatic operation, the magnetic tape cassette 220 held by the bucket 202 is angularly moved into the cassette loading portion 205 defined by the recess. At this time, the positioning pins 207a and 207b are slidingly inserted into their mating positioning holes 221a and 221b, respectively, and-the capstan 208 is loosely fitted in the mating capstan insertion hole 222.
Therefore, the inner peripheral surfaces of the positioning holes 221a and 221b are rubbed by the positioning pins 207a and 207b, respectively, each time the magnetic tape cassette 220 is loaded and unloaded.
As explained above, the cassette case of the magnetic tape cassette 220 is generally molded of a resin such as an ABS resin or a PS resin because of its processability and low cost. Therefore, when the cassette case is subjected to repeated rubbing action as encountered with the inner peripheral surfaces of the positioning holes 221a and 221b, the cassette case is gradually worn because these resins are inferior in wear resistance.
As a result, the positioning holes 221a and 221b become deformed, and hence the magnetic tape cassette fails to be accurately loaded in position into the cassette loading portion, thereby adversely affecting the proper positional relation between the magnetic head and the cassette. This causes various tape running problems such as improper contact between the tape and the magnetic head, which results in an unstable reproduction output, and signal dropout due to the adhering to the magnetic tape 24 of powder produced as a result of the above rubbing action.
Further, a magnetic tape cassette for use in audio equipment, when stored, is usually contained in a magnetic tape cassette storage case made of a plastics material.
The magnetic tape cassette has openings for receiving a magnetic head, etc., of a recording and playback device, and the magnetic tape extends across these openings. The storage case prevents dust from entering the cassette during storage, protects those portions of the magnetic tape disposed in the above openings, and protects the whole of the cassette.
There are various known shapes and constructions of storage cases. Generally, the storage case has a lid having a pocket for holding the cassette, and a casing having a pair of rotation preventing lugs for insertion into respective shaft insertion holes of the magnetic tape cassette.
Pivot pins formed respectively on right and left side walls of the casing are fitted in respective holes formed through right and left side walls of the lid so that the lid and the casing can be opened and closed relative to each other similar to a door.
Further, the casing has retainer projections, and the lid has engaging holes with which the retainer projections are engaged when the lid is closed relative to the casing, thereby holding the lid against accidental opening movement.
In view of the manufacturing cost, the casing and the lid are generally made of an acrylonitrile styrene (AS) resin, PS resin, polypropylene (PP) resin or the like.
The storage case is opened and closed each time the magnetic tape cassette is placed in storage and removed therefrom. Storage cases quite often rub together during times when they are stored and carried. When the storage case is opened and closed, the pivot pins are angularly moved within their respective mating holes, and the pivot pin and the peripheral surface of the hole rub together, producing rubbed-off powder. With respect to the retainer projections and the engaging holes, a similar rubbing action occurs to further produce rubbed-off powder. Such rubbed-off powder is a fine powder and therefore is liable to be dispersed within the storage case to adhere to the surface of the magnetic tape exposed through the above-mentioned openings. As a result, recording and playback cannot be effected at those portions of the magnetic tape to which the rubbed-off powder adheres as signal dropout occurs. In the event of such signal dropout, as described in TELEVISION TECHNOLOGY, (September 1985, page 34, a Japanese journal published by Denshi Gijutsu Shuppan K. K.) picture flicking occurs and the reproduced audio is noisy.
Thus, despite the fact that the storage case of a conventional design was originally intended to protect the magnetic tape cassette and to provide dust prevention, rubbed-off powder can still be produced over long periods of time.
The above-mentioned AS, PS and PP resins have a low surface hardness (strength), and therefore when the storage cases rub together during storage and carrying, the surface thereof is susceptible to damage. An index card indicative of the contents of the recorded information is often contained within the storage case. If there are scratches on the case surface, the index card and an index bonded to the cassette surface can be obscured. Such a phenomenon is also undesirable from the viewpoint of appearance. Thus, these problems have made it quite difficult to use a storage case for a long period of time.
In view of the above, it has been proposed to provide ribs on marginal portions of the outer surface of the storage case so that the outer surfaces of the storage cases do not contact each other. However, this has been found not sufficient for the prevention of scratching. On the contrary, providing ribs reduces the area of contact between the adjacent storage cases, and therefore they are liable to slide with respect to each other. As a result, the incidence of accidental dropping and damage is increased.
Also, in magnetic tape cassettes, the magnetic tape wound on the pair of tape winding bodies is rotatably mounted within a cassette case composed of upper and lower cassette halves, each of a one-piece molded construction made of a synthetic resin.
One particular tape winding body used in a video tape cassette has upper and lower flanges formed respectively on upper and lower ends of the tape reel to prevent the lateral edges of the magnetic tape from contacting the inner surfaces of the cassette halves and also to regulate the position of winding of the tape so as to maintain even tape winding. A tape winding body of another type, such as one used in an audio tape cassette, has a pair of upper and lower friction sheets each mounted between the end face of the hub and the inner surface of the cassette half to reduce the amount of friction between the lateral edge of the magnetic tape and the inner surface of the cassette half to thereby stabilize the running of the magnetic tape and also to maintain even tape winding.
Each of the hubs is rotatably supported by respective cylindrical spool support walls formed on the upper and lower cassette halves in such a manner that the hub is prevented from moving in the horizontal direction with respect to the cassette. As a result, however, the upper and lower portions of the inner periphery of the hub are always rubbed by the corresponding spool support walls.
The flanged tape reel has a projection formed at an upper surface thereof and disposed at its axis. A metal plate mounted on the upper cassette half urges this projection inwardly of the cassette so as to limit the vertical movement of the tape reel. Further, the outer peripheral edges of the flanges of the tape reel contact the side walls of the cassette halves to limit the horizontal movement of the tape reel.
Therefore, due to vibration and shock occurring, for example, during transportation of the cassette, the outer peripheral edges of the flanges of the flanged tape reel are rubbed by the above side walls, and the outer surface of the lower flange is rubbed by the inner surface of the lower cassette half.
As already discussed, cassette cases have recently been molded of a general-purpose resin of inferior wear resistance such as ABS and PS resin because of its processability and reduced manufacturing cost. On the other hand, the tape winding bodies such as the above-mentioned hub and flanged tape reel are generally molded of a resin of high wear resistance such as a polyoxymethylene resin. Therefore, the cassette case is gradually worn.
As a result, the spool support walls are deformed, and hence the axis of rotation of the tape reel can deviate during rotation, which results in unstable running of the magnetic tape. Further, the rubbed-off powder resulting from this action adheres to the magnetic tape, causing various tape troubles such as signal dropout.
Yet further, the invention relates to a magnetic tape cassette incorporating a pad for stabilizing the running of a magnetic tape.
Magnetic tape cassettes for audio and video use are provided with guide members such as an immovable tape guide in sliding contact with the magnetic tape and a guide roller rotatably engaged with the magnetic tape to guide the running of the tape. These guide members are arranged to contact with either the backside (the base side) or the front side (the magnetic layer side) of the magnetic tape. Particularly, the rotatable guide roller is used mainly because it can avoid unnecessary frictional sliding contact with the magnetic tape. Particularly, recently high-density magnetic tapes have been used, and therefore such a rotatable guide roller has been increasingly used to avoid signal dropout caused by scuffing of the magnetic tape as a result of direct sliding contact of the magnetic tape and an immovable tape guide.
Such guide rollers are of a cylindrical shape, and some have a flange at their lower end. Generally, the guide roller is made of a plastics material having a relatively high wear resistance, such as POM resin. The magnetic tape is in sliding contact with the outer periphery of the guide roller, that is, the tape extends around the guide roller through a certain angle, and therefore the guide roller considerably influences the running of the magnetic tape. There are occasions when slippage occurs between the magnetic tape and the reels around which the tape is wound when the tape is stopped subsequent to a fast-forwarding operation to thereby displace the magnetic tape out of position. As a result, the magnetic tape can accidentally project from the tape extraction opening of the cassette, subjecting it to damage. This tendency is particularly marked in cassettes incorporating a rotatable roller.
To avoid such problems, a pad is provided within the cassette for urging the magnetic tape against the tape guide or the rotatable roller.
For example, such a pad may be molded of a plastics material, and be resilient, short and thin. The pad is fixedly secured at one end and urged into a curved configuration to have an elastic force so that the pad urges the magnetic tape against the guide roller.
Generally, the pad has a plate-like base molded of polyethylene terephthalate (PET) resin and a layer of ultra-high-molecular-weight polyethylene or Teflon formed on the base. Polyethylene terephthalate resin has the drawback that it is inferior in wear resistance. Ultra-high-molecular-weight polyethylene and Teflon though are expensive materials and therefore the pad has generally been costly because of its material cost and processing cost.
To reduce the cost, it has been proposed to provide a one-piece molded plate made solely of ultra-high-molecular-weight polyethylene. Although such a pad is superior in wear resistance with respect to sliding contact with the magnetic tape, it is inferior in resistance to creep. Therefore, there have been encountered problems such as an unstable urging force applied to the magnetic tape.
The invention yet further relates to a magnetic tape cassette having a transparent window provided in cassette case body.
The shape and appearance of audio and video magnetic tape cassettes vary depending on their use. Despite this, magnetic tape cassettes have a common feature in that they are usually provided with a transparent window for viewing the interior of the magnetic tape cassette.
The transparent window is very useful for observing the winding condition of the magnetic tape and for estimating the present recording and playback position, and it is not too much to say that a transparent window is an indispensable feature in a magnetic tape cassette.
FIG. 2 illustrates an example of a method for forming a conventional transparent window. In this method, an opening 602 serving as the window is formed at a predetermined position in an upper cassette half 601 made, for example, of an ABS resin. A stepped portion 605 stepped in the direction of the thickness of the cassette is provided around the opening 602. A plate 603 of a transparent synthetic resin having a stepped portion 606 complementary in shape to the stepped portion 605 is fusingly bonded to the edge portion of the opening 602 to form the transparent window.
The plate 603 is fusingly bonded to the edge portion of the opening 602 usually by ultrasonic bonding. More specifically, a projection or fusion rib 604 is formed on the stepped portion 606 formed on the lower surface of the plate 603. The projection 604 is brought into contact with the stepped portion 605 defining the edge portion of the opening 602, and then ultrasonic energy is applied to this contact region so that the projection 604 is fused to bond together the plate 603 and the edge portion of the opening 602.
In such ultrasonic bonding, as the area of contact between two parts to be bonded together increases, the time required to effect fusion bonding is increased, lowering the operating efficiency.
For this reason, the projection 604 serving as the fusion rib is provided. However, as a result of the provision of the projection 604, the height A used for positioning the fitting portion 607 of the plate 603 is reduced by an amount corresponding to the height of the projection 604. This makes it difficult to position the plate 603 with respect to the opening 602 when the former is fitted in the latter. In addition, when ultrasonic energy is applied to the fusion portion to effect ultrasonic bonding, the plate 603 is subjected to vibration. As a result, the shoulder of the fitting portion 607 sometime rides on the stepped portion 605 damaging the plate 603.
Although it can be considered to thicken the plate 603 in order to overcome the above problems, this is not desirable because it lowers the transparency of the window and increases the cost. In addition, since the plate 603 is subject to vibration upon application of ultrasonic energy to the fusion portion during the ultrasonic bonding, it is difficult to accurately determine the size of the opening 602. For this reason, it has been necessary to make the size of the opening larger, taking the vibration of the plate 603 into account. As a result, upon assembly, there is created a gap between the fitting portion 607 and the edge of the opening 602. Further, when the magnetic tape cassette is carried or when it is stored on a rack, the surface of the plate 603 is susceptible to damage such as by scratching, and the transparency of the window can thereby be lowered.
Thus, there is a problem in that the overall appearance of the magnetic tape cassette can readily be marred.
Moreover, the invention relates to a magnetic tape cassette having a guide member for stabilizing the running of the magnetic tape in the cassette.
Magnetic tape cassettes for audio and video use are provided with guide members such as an immovable tape guide in sliding contact with the magnetic tape and guide roller rotatably engaged with the magnetic tape to guide the running of the tape. These guide members are arranged in contact with either the backside (the base side) or the front side (the magnetic layer side) of the magnetic tape. Particularly, the rotatable guide roller is used mainly because its use avoids unnecessary frictional sliding contact with the magnetic tape.
As discussed above, such guide members are generally of a cylindrical shape, and some have a flange at its lower end or flanges at its upper and lower ends, respectively. Generally, the guide member is made of a plastics material having a relatively high wear resistance, such as a POM resin. The magnetic tape is in sliding contact with the outer periphery of the guide member, that is, the tape extends around the guide member through a certain angle, and therefore the guide member considerably influences the running of the magnetic tape. Recently, a recording and playback device as well as a magnetic tape cassette has been required to have a high performance to meet a high density recording and playback, and accordingly the guide member has been required to have an improved performance. Particularly, in video tape cassettes of the type in which recording and playback are effected digitally, the problem of the tape running has become important.
A magnetic tape cassette having the above-mentioned guide member is described, for example, in TELEVISION TECHNOLOGY, December 1986, page 45 (see, in particular, FIG. 20 of this article).
The guide member is made of a POM resin as described above. One problem is that the use of a resin of a high wear resistance such as a POM resin increases the cost of the cassette. Such a guide member of high wear resistance can be produced at a lower cost by molding a hollow or solid cylindrical body using a more inexpensive resin, and coating an ultraviolet-curing coating onto the outer peripheral surface of the cylindrical body with which the magnetic tape is to be disposed in sliding contact.
However, since the surface electrical resistance of a resin subjected to ultraviolet-curing is very high, static electricity is liable to develop when the magnetic tape is moved in sliding contact with the outer surface of the guide member. This causes a problem in that the magnetic tape is then undesirably attracted to the surface of the guide member because of the static electric charge, thus rendering the tape running unstable.